1. Field of the Invention
The present invention relates to an image lens system, and more particularly, to a compact image lens system used in electronic products.
2. Description of the Prior Art
In recent years, with the popularity of portable electronic products having photographing function, the demand of compact imaging lens system has grown. Generally, the sensor of a general photographing camera is none other than CCD (Charge Coupled Device) or CMOS device (Complementary Metal Oxide Semiconductor device). Furthermore, advances in semiconductor manufacturing technology have allowed the pixel size of sensors to be reduced and therefore lead compact imaging lens systems to higher resolution. In the meantime, the demand for better image quality is also increased.
A conventional compact imaging lens system equipped on a portable electronic product is often composed of three lens elements such as the lens system set forth in U.S. Pat. No. 7,184,225, comprising, in order from an object side to an image side: a first lens element with positive refractive power, a second lens element with positive refractive power and a third lens element with negative refractive power. Because the progression of manufacturing technology and the trend of being compact for electrical products, the pixel size of sensors is continuously required to be reduced and the demand of the image quality of system is getting higher and higher; therefore, the conventional three-lens-element system can no longer satisfy optical systems of even higher level.
In order to satisfy demands of higher level, a conventional imaging lens system with high resolving power, such as the one set forth in U.S. Pat. No. 7,365,920, generally has a front stop and four lens elements; wherein, the first and second lens elements are adhered together to form a doublet for correcting the chromatic aberration. However, this kind of arrangement has the following disadvantages. First, the degree of freedom in arranging the lens system is curtailed due to the employment of excessive number of spherical glass lenses; thus, the total track length of the system cannot be reduced easily. Second, the process of adhering glass lenses together is complicated, posing difficulties in manufacturing. Moreover, because the size of lens system is getting smaller, multiple reflection of unnecessary light in the lens tube is often caused as such compact lens system is configured in such limited space, and the imaging is also affected. Therefore, it is extremely important to well-design the optical configuration to avoid unnecessary light from entering the imaging area. To sum up, a need is continuously existed for a lens system with good image quality and moderate total track length and is suitable for compact and portable electronic products.